Is this arching wrong ?

[Dr. Mark]

Using a line through the midpoint of the ribs along the long axis of symmetry seems like a good convention to use - call it x1.  The vertical axis is a little problematic - simplest would a line normal to x1 and at, say, the midpoint of the body, but consider also that the string force is applied at the bridge.  I believe (correct me if I'm wrong) the bridge is set so as to create no frictional forces parallel to the plate tangent at the bridge feet, which means that force applied to the belly through the bridge is normal to the tangent at the bridge but may not be normal to x1.  A problem also arises if we use an axis through the apex of the belly since it may not be the apex of the back, and it also may not be independent of stress condition and models.  So a good convention may be to assign an axis x2 normal to x1 and through the longitudinal midpoint of the belly.  A transverse axis x3  then should be normal to the (x1,x2) plane using the right-hand rule to complete a right-hand Cartesian coordinate frame.  It seems such a convention would simplify discussion and comparisons of various ideas.  Any results could also be transformed comparatively easily to any other system we would want to use for illustrative or other purposes.

Alternatively, the long axis could be along the centerline and fixed vertically where the back plate surface would contact supports at two points, say at the button and just below the endpin.  The frame is then a simple translation in the -x2 direction from the above with perhaps a slight rotation depending on the lower and upper rib heights.  We may want to assume that the violin is only supported normal to x2 with this frame while being otherwise free to translate and rotate along both x1 and x3.

Just noting that trying to hold a discussion among N people with each using a unique frame of reference - or worse, an unspecified and arbitrary frame, is the recipe for disaster, described in Genesis as chosen by the Almighty to confound the Babylonians.

 

Edited December 13, 2023 by Dr. Mark
Clean up

[reguz]

3 hours ago, Peter K-G said:

Those images are from reguz website, just trying to move the discussion forward.

I have no clear opinion, other than it feels over simplified. Things happens in 3D.

It cannot be explained only from 2D side view and lengthwise deformation.

Peter, Youmay read the master result. Look especially from page 67. there you cansee the 3D esult and what they found out about the STLs Al is based on the plates I made for this work.

web5247.pdf

[reguz]

42 minutes ago, Dr. Mark said:

Using a line through the midpoint of the ribs along the long axis of symmetry seems like a good convention to use - call it x1.  The vertical axis is a little problematic - simplest would a line normal to x1 and at, say, the midpoint of the body, but consider also that the string force is applied at the bridge.  I believe (correct me if I'm wrong) the bridge is set so as to create no frictional forces parallel to the plate tangent at the bridge feet, which means that force applied to the belly through the bridge is normal to the tangent at the bridge but may not be normal to x1.  A problem also arises if we use an axis through the apex of the belly since it may not be the apex of the back, and it also may not be independent of stress condition and models.  So a good convention may be to assign an axis x2 normal to x1 and through the longitudinal midpoint of the belly.  A transverse axis x3  then should be normal to the (x1,x2) using by the right-hand rule to complete a right-hand Cartesian coordinate frame.  It seems such a convention would simplify discussion and comparisons of various ideas.  Any results could also be transformed comparatively easily to any other system we would want to use for illustrative or other purposes.

Alternatively, the long axis could be along the centerline and back plate surface at the button and below the endpin.  The frame is then a simple translation in the -x2 direction from the above.  We may want to assume that the violin is only supported normal to x2 with this frame while being free to translate and rotate along both x1 and x3.

Just noting that trying to hold a discussion among N people with each using a unique frame of reference is the recipe for disaster described in Genesis as chosen by the Almighty to confound the Babylonians.

 

Thank you Mark for your opinion how to look and handle circumstances. But all must also inclode the frame work I found and the Master disartation give proof that the STL (in and out side as they are at the same location are very strong)  has graet influence on what may happen. Just take another look at the holographic image from the back. We seen two mode 5 and the mode 2 at the same time due to the frame work. We also see that the location similar the sound post moves which I described in this thread.

[David Burgess]

36 minutes ago, reguz said:

We also see that the location similar the sound post moves

Yup. So why are you continuing to insist that the soundpost location must be the stationary reference point?

 

40 minutes ago, reguz said:

But all must also inclode the frame work I found

Uh, no!
Get a grip on reality dude. Someone disagreeing with you does not automatically make them wrong, regardless of whatever misplaced belief you may have about yourself being "Captain Of The Universe".

[Anders Buen]

59 minutes ago, reguz said:

Thank you Mark for your opinion how to look and handle circumstances. But all must also inclode the frame work I found and the Master disartation give proof that the STL (in and out side as they are at the same location are very strong)  has graet influence on what may happen. Just take another look at the holographic image from the back. We seen two mode 5 and the mode 2 at the same time due to the frame work. We also see that the location similar the sound post moves which I described in this thread.

I do not think you can see mode 2 or 5 here. This appear to be a deflection pattern under a load or from changes in humidity. Holographic monitoring like this does either measure the deflection or the vibration amplitudes. I used such a system during my master thesis to monoitor vibrations and their shapes.

[David Burgess]

20 minutes ago, Anders Buen said:

I do not think you can see mode 2 or 5 here. This appear to be a deflection pattern under a load or from changes in humidity. Holographic monitoring like this does either measure the deflection or the vibration amplitudes. I used such a system during my master thesis to monoitor vibrations and their shapes.

It could also be a representation of the deflection taking place with the longitudinal air "sloshing mode", which emits a little bit of sound on some  violins, while on other violins, hardly any. I too am not seeing either mode 2 or 5.

[Anders Buen]

55 minutes ago, David Burgess said:

It could also be a representation of the deflection taking place with the longitudinal air "sloshing mode", which emits a little bit of sound on some  violins, while on other violins, hardly any. I too am not seeing either mode 2 or 5.

Quite possible, if this is a vibration picture. 

[sospiri]

11 hours ago, Andreas Preuss said:

I am sure that all what Antonio Stradivari did on his instruments was for good reasons and it worked as a whole. But this doesn’t mean that it’s the only possible solution. 
 

In my view a few classical constructional features came from practical and/or aesthetic considerations rather than pure acoustical considerations. 

 

I believe that Stradivari did make his ribs and linings the way he did to enhance acoustic properties. 

To be able to vibrate and twist freely between the corners. 

[Dennis J]

10 hours ago, reguz said:

Peter, Youmay read the master result. Look especially from page 67. there you cansee the 3D esult and what they found out about the STLs Al is based on the plates I made for this work.

web5247.pdf 19.32 MB · 2 downloads

Looking at the drawn STLs on the plate I can see that they neatly skirt the ends of the sound holes.

And something I think significant is how the STLs intersect the upper and lower bout inflection points. However not matching (the distance from longitudinal centre) any of the central arch inflection points both top and back doesn't make much sense. The only way to do that is to design templates which have matching top and back inflection points so their archings are synchronised in that way. 

Testing a back plate arching which is nearly finished with a short ruler from the bridge centre to the inflection points I find the lower bout one close to straight but the upper bout one out quite a bit. I'm not sure how it will turn out when I finish scraping. Trying to get straight STLs could involve outline shape and long arch design as well as longitudinal proportionality around body length and bout widths. But I won't be trying to manipulate any arching to achieve that outcome. It sounds totally impractical.

 

 

Edited December 13, 2023 by Dennis J
Rewording

[Peter K-G]

10 hours ago, reguz said:

Peter, Youmay read the master result. Look especially from page 67. there you cansee the 3D esult and what they found out about the STLs Al is based on the plates I made for this work.

web5247.pdf 19.32 MB · 4 downloads

I have read this before, can't see any new findings. To my it  looks like any repetitive study on the modes. I find Strad 3D much more enlightening.

[reguz]

8 hours ago, Dennis J said:

Looking at the drawn STLs on the plate I can see that they neatly skirt the ends of the sound holes.

And something I think significant is how the STLs intersect the upper and lower bout inflection points. However not matching (the distance from longitudinal centre) any of the central arch inflection points both top and back doesn't make much sense. The only way to do that is to design templates which have matching top and back inflection points so their archings are synchronised in that way. 

Testing a back plate arching which is nearly finished with a short ruler from the bridge centre to the inflection points I find the lower bout one close to straight but the upper bout one out quite a bit. I'm not sure how it will turn out when I finish scraping. Trying to get straight STLs could involve outline shape and long arch design as well as longitudinal proportionality around body length and bout widths. But I won't be trying to manipulate any arching to achieve that outcome. It sounds totally impractical.

 

 

This was kind of you responding as you do. However, remember that the STLs I found by pure calculation of the geometric shape. So, my interrest is finding out by practical making how the dynamic result will become. I ( I say we) have good experience so I have not thought about locate the STLs in other direction. However, I am sure it will affet the result wich of course can be better. Thank you for your describtion.

[reguz]

4 hours ago, Peter K-G said:

I have read this before, can't see any new findings. To my it  looks like any repetitive study on the modes. I find Strad 3D much more enlightening.

No ofcourse there is nothing new in this . It's the result of practical making and calculation with a FEA.

[reguz]

12 hours ago, sospiri said:

I believe that Stradivari did make his ribs and linings the way he did to enhance acoustic properties. 

To be able to vibrate and twist freely between the corners. 

In a workshop in Cremona attending of 17 makers at Toto's place we checked the locations of the STL on their plates. Only one had exactly location compared with the geometric model. How was that possible? Well Toto came with a caster plast of a Stradivari instrument. He had made the "six" for shaping the arching and came out with the STLs as they are on the geometric model. We became very surprised. How could this be?

It is an experience learning that STLs are on the Strad caster plast as I found them by geometric constructing.

It could be possible that Strad gave his workers the templates to work and shape after. Well done Strad checked the result of the STLs and probably made some corrections.

What however is important is that also on the inside there must be made STL shape at the same location. First in that state we have a "beam" that make part of the octrahedrone Framework.

This was tested in the master dissertation and found that the straight STL condition remain. So, it is given proof that the framework function and thus the behavior of the bout shapes that become deflected. 

Having this result, we may start thinking of how graduating the thickness in relation to that shape and the wood quality. The result comes from experimenting

[reguz]

12 hours ago, Anders Buen said:

Quite possible, if this is a vibration picture. 

No Anders. This holographic picture is made by laying two pictures above each other. The stressed instrument with string load and after that an increasing string load by rotating the fine tuner 4 degree.

The new condition is laid on the first and we see the not deflecting structure (black) and the deflecting structure. We can observe that there is some unbalance on the bout shape.

What the image tells us furthermore is that the stress condition has changed. This means i "Spring" function is present. Do we release the increased stress the figure will show a total white image,

Just the function of "SPRING” when we start playing the instrument is important. It produces the underlaying dynamic behavior. The belly will show equal conditions. If we look at the structure of the spruce wood we see small beams, the winter grown wood. The become stress by buckling. It is important that they have curve shape otherwise the only become compressed. 

I try to come to the understanding whet this means for the possible mode shapes area that may arise by spontaneous responding on a specific frequency. A number of such winter grown beams will do and shift by different frequency.

Working together with Staffan Borseman (former concert master of  Danmarks Radios symfoniorkester Orkester)

 We tested scraping on the surface and thus produced different stress condition on buckling curved beams with a tonal changing result. We could make WULF condition but this was easy removing by scarping on the bout

Four violin where made by Odvar Eiken. These instrument now are in Norway. They are the best he made

[Anders Buen]

5 hours ago, reguz said:

No Anders. This holographic picture is made by laying two pictures above each other. The stressed instrument with string load and after that an increasing string load by rotating the fine tuner 4 degree.

Can be interferometry between a reference and a changed situation, like by stress. I know they can use heat as well for excitation of special laminates, like plane- or other aviation parts, for discovering possible faults or voids inside. This system is extremely sensitive and tests needs to be done on a special vibration insulated table. The «metric» is a few nanometres, depending on the light used and how many fringes the framegrabber can work with. For simplicity say: 30-300 nm, about half the wavelength of green laser light.

No instruments becomes better from just being exposed to exotic measurement systems. One needs to be really impressed by sceince and technology, and maybe seeing your own instrument through it, to beleive it contributed to improved sound and performance. 

 

[Peter K-G]

6 hours ago, reguz said:

Well Toto came with a caster plast of a Stradivari instrument. He had made the "six" for shaping the arching and came out with the STLs as they are on the geometric model. We became very surprised. How could this be?

It is an experience learning that STLs are on the Strad caster plast as I found them by geometric constructing.

It could be possible that Strad gave his workers the templates to work and shape after. Well done Strad checked the result of the STLs and probably made some corrections.

There could be a much simpler explenation.

Once you realize how to make them look in a certain way, which is developing knowledge of a visual 3D shape, that is linked to the plate outline and in combination with working metod, will automatically give STL:s like you describe.

And it is no coincident that this shape would be a good structure that can be found by engineering a model.

[Dr. Mark]

22 hours ago, reguz said:

But all must also inclode the frame work I found and the Master disartation give proof that the STL...[etc]

The subject of my preceding statement concerned choosing a reference frame.  In order to make your assertion (above) I have to assume that you either a) misunderstand what a reference frame is, or b) you're so intent on pushing an agenda that you don't care whether your comment is appropriate to the topic.  I hope you don't think that the length of your nose in a photograph affects the length of your nose.

[Andreas Preuss]

9 hours ago, reguz said:

It is an experience learning that STLs are on the Strad caster plast as I found them by geometric constructing.

Would it be asking too much to know which instrument by Antonio Stradivari this was?

[reguz]

56 minutes ago, Andreas Preuss said:

Would it be asking too much to know which instrument by Antonio Stradivari this was?

THis was at  at Fransesco Toto workshop 17-04-2012. At that timem his email was

TOTO@violintrtade.com. I believe it is best you ask him yourselve.

[Andreas Preuss]

9 hours ago, reguz said:

We tested scraping on the surface and thus produced different stress condition on buckling curved beams with a tonal changing result. We could make WULF condition but this was easy removing by scarping on the bout

Do you have any sound graphs which can show the difference?

BTW there are many first class instruments which have a strong wolf resonance.

[reguz]

2 hours ago, Dr. Mark said:

The subject of my preceding statement concerned choosing a reference frame.  In order to make your assertion (above) I have to assume that you either a) misunderstand what a reference frame is, or b) you're so intent on pushing an agenda that you don't care whether your comment is appropriate to the topic.  I hope you don't think that the length of your nose in a photograph affects the length of your nose.

My reference is the sound post. This is not a frame. But you may explain what you see as a frame. I do not understand.

[reguz]

1 minute ago, Andreas Preuss said:

Do you have any sound graphs which can show the difference?

BTW there are many first class instruments which have a strong wolf resonance.

No we never make recordings of the WULF

[reguz]

3 hours ago, Peter K-G said:

There could be a much simpler explenation.

Once you realize how to make them look in a certain way, which is developing knowledge of a visual 3D shape, that is linked to the plate outline and in combination with working metod, will automatically give STL:s like you describe.

And it is no coincident that this shape would be a good structure that can be found by engineering a model.

In the begining I searched for special conditions as I described and well found I liked to find if the geometry also produce STL condition which it does. Yes STL on arching shape arises on many diffrent location depending how you shape your arching, This we looked at in the workshop of TOTO as decribed earlier

[reguz]

9 minutes ago, Andreas Preuss said:

Do you have any sound graphs which can show the difference?

BTW there are many first class instruments which have a strong wolf resonance.

Working together with Staffan Borseman we got clear results so we learned what was possible to do but we never recorded the result.

[reguz]

4 hours ago, Anders Buen said:

Can be interferometry between a reference and a changed situation, like by stress. I know they can use heat as well for excitation of special laminates, like plane- or other aviation parts, for discovering possible faults or voids inside. This system is extremely sensitive and tests needs to be done on a special vibration insulated table. The «metric» is a few nanometres, depending on the light used and how many fringes the framegrabber can work with. For simplicity say: 30-300 nm, about half the wavelength of green laser light.

No instruments becomes better from just being exposed to exotic measurement systems. One needs to be really impressed by sceince and technology, and maybe seeing your own instrument through it, to beleive it contributed to improved sound and performance.